For many years, manufacturers and users of skis have understood that weight, length, and strength are not the only characteristics that affect the performance of the skis in action. In particular, it has become widely appreciated that the flexibility of the skis is an important factor in determining the ease with which the ski may be turned and with which a turn may be maintained by the ski once the turn has been entered. Furthermore, it is well known that the flexibility of the forebody of the ski should not necessarily be the same as the flexibility of the afterbody of the ski. Still further, it is axiomatic that both the flexural and the torsional flexibilities or stiffnesses of the skis are important. Flexural bending takes place about an axis perpendicular to the longitudinal axis of the ski, whereas torsional bending takes place about an axis substantially coincident with the longitudinal axis of the ski.
The measurements of both flexural stiffness, or spring constant, and torsional stiffness of skis are the subjects of test standards promulgated by the American Society for Testing and Materials. A Standard Test Method for Center Spring Constant and Spring Constant Balance of Alpine Skis was published by the American Society for Testing and Materials Committee on Standards in 1977 (Designation F-498-77-Reapproved 1988.) A Standard Test Method for Torsion Characteristic of Alpine Skis was published by the American Society for Testing and Materials in 1982 (Designation F-779-82-Reapproved 1988). As implied by the aforementioned titles, the thrust of those two standard test methods is a determination of spring constants, one for flexural deformation and the other of torsional deformation.
While the determination of such spring constants was a step forward, it did not provide information of the type which is most useful in the matching of skis to form a pair or in the selection of skis to conform to the preferences of individual skiers, so far as ease of entry into turns and maintenance of turns were concerned. Moreover, the procedure in accordance with those standard test methods attempted to isolate the forebody of the ski from the afterbody of the ski for the purposes of measurement. However, in use, the flexibility of the forebody and that of the afterbody influence each other because bending moments and torsional forces are transmitted between the forebody and the afterbody through the "waist" of the ski, whereon the binding is mounted and the weight of the skier is carried. Further, the data produced by the standard test methods were not so immediately useful to a person selecting skis for a pair or determining the effect of use of the skis and passage of time upon their flexural and torsional stiffness and flexibility. Accordingly, it appears that the prior art, as represented by the aforementioned standards the American Society for Testing and Materials, is deficient in one or more important ways.